As measures against global warming and for energy saving, expectations for distributed power generation, including wind power generation, small hydroelectric power generation, and micro gas turbine power generation, are growing, and to ensure distributed power generation, the demand for small-to-medium-capacity generators is expanding. With generators for wind power generation and small hydroelectric power generation, in particular, since systems need to be downsized, expensive rare-earth magnets are generally used.
Meanwhile, to ensure power generation from low speed and minimize cogging torque and torque ripple, generators having no core, coreless-type generators as they are called, are regarded as promising. Generally, cogging torque is defined as torque pulsation that occurs in a state where winding is opened, namely where winding current is not fed. When a rotor is rotated, magnets and core are attracted to each other, thus causing cogging torque. Meanwhile, torque ripple is defined as torque pulsation that occurs in a state where a load is connected to the winding, namely where winding current is fed. When the rotor is rotated, interaction between magnets, core, and the magnetic force due to winding current generates torque ripple.
Patent Literature 3 discloses a reluctance motor comprising a stator having wire-wound salient poles and a rotor having salient poles, wherein the sharp edge at one of the end faces of the salient pole of the stator and that of the rotor are chamfered to prevent high harmonic component from being contained in the inductance of the winding.
Patent Literature 4 discloses a generator a stator and a rotor, wherein cutouts are provided asymmetrically at the tip of the salient poles of the rotor, and wherein torque ripple generated at the time of regenerating operation is reduced by the effect of these cutouts.